The Art of Thinking Clearly: Better Thinking, Better Decisions

participants would have preferred to drop out of the vicious cycle years ago.
In much the same way, if someone approaches you in the supermarket,
whether to offer you a taste of wine, a chunk of cheese or a handful of olives, my
best advice is to refuse their offer – unless you want to end up with a refrigerator
full of stuff you don’t even like.
See also Framing (ch. 42); Incentive Super-Response Tendency (ch. 18); Liking Bias
(ch. 22); Motivation Crowding (ch. 56)

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7
BEWARE THE ‘SPECIAL CASE’
Confirmation Bias (Part 1)
Gil wants to lose weight. He selects a particular diet and checks his progress on
the scales every morning. If he has lost weight, he pats himself on the back and
considers the diet a success. If he has gained weight, he writes it off as a normal
fluctuation and forgets about it. For months, he lives under the illusion that the diet
is working, even though his weight remains constant. Gil is a victim of the
confirmation bias
– albeit a harmless form of it.
The 
confirmation bias
is the mother of all misconceptions. It is the tendency to
interpret new information so that it becomes compatible with our existing theories,
beliefs and convictions. In other words, we filter out any new information that
contradicts our existing views (‘disconfirming evidence’). This is a dangerous
practice. ‘Facts do not cease to exist because they are ignored,’ said writer
Aldous Huxley. However, we do exactly that, as super-investor Warren Buffett
knows: ‘What the human being is best at doing, is interpreting all new information
so that their prior conclusions remain intact.’
The 
confirmation bias
is alive and well in the business world. One example: an
executive team decides on a new strategy. The team enthusiastically celebrates
any sign that the strategy is a success. Everywhere the executives look, they see
plenty of confirming evidence, while indications to the contrary remain unseen or
are quickly dismissed as ‘exceptions’ or ‘special cases’. They have become blind
to disconfirming evidence.
What can you do? If the word ‘exception’ crops up, prick up your ears. Often it
hides the presence of disconfirming evidence. It pays to listen to Charles Darwin:
from his youth, he set out systematically to fight the 
confirmation bias
. Whenever
observations contradicted his theory, he took them very seriously and noted them
down immediately. He knew that the brain actively ‘forgets’ disconfirming
evidence after a short time. The more correct he judged his theory to be, the more
actively he looked for contradictions.
The following experiment shows how much effort it takes to question your own
theory. A professor presented his students with the number sequence 2–4–6.

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They had to calculate the underlying rule that the professor had written on the
back of a sheet of paper. The students had to provide the next number in the
sequence, to which the professor would reply ‘fits the rule’ or ‘does not fit the
rule’. The students could guess as many numbers as they wanted, but could try to
identify the rule only once. Most students suggested 8 as the next number, and
the professor replied: ‘Fits the rule.’ To be sure, they tried 10, 12 and 14. The
professor replied each time: ‘Fits the rule.’ The students concluded that: ‘The rule
is to add two to the last number.’ The professor shook his head: ‘That is not the
rule.’
One shrewd student tried a different approach. He tested out the number -2.
The professor said ‘Does not fit the rule.’ ‘Seven?’ he asked. ‘Fits the rule.’ The
student tried all sorts of numbers -24, 9, -43?. . .?Apparently he had an idea, and
he was trying to find a flaw with it. Only when he could no longer find a counter-
example, the student said: ‘The rule is this: the next number must be higher than
the previous one.’ The professor turned over the sheet of paper, and this was
exactly what he’d written down.
What distinguished the resourceful student from the others? While the majority
of students sought merely to confirm their theories, he tried to find fault with his,
consciously looking for disconfirming evidence. You might think: ‘Good for him,
but not the end of the world for the others.’ However, falling for the 
confirmation
bias
is not a petty intellectual offence. How it affects our lives will be revealed in
the next chapter.